Histologic classification and staging of gestational trophoblastic disease.

Gestational trophoblastic disease (GTD) forms a heterogeneous group of interrelated lesions which are characterized by an abnormal proliferation of the different types of trophoblastic epithelium. Complete hydatidiform moles represent a noninvasive placental disease that is characterized by hydropic swelling of the chorionic villi with marked trophoblastic proliferation. The partial mole contains two populations of villi: one of normal size, the other hydropic with less marked trophoblastic hyperplasia. The risk of developing persistent GTD is very low. Choriocarcinomas represent an avillous invasive proliferation of trophoblastic cells surrounded by necroses and hemorrhages displaying a dimorphic pattern with early vascular invasion and hematogeneous metastatic spread. Placental site trophoblastic tumor (PSTT) resembles the rarest form of GTD. In its cellular composition, PSTT preferentially contains intermediate trophoblastic cells with typically positive hPL-immunostaining. Mostly, PSTT's are benign tumors, but malignant cases are well known. Miscelleanous forms of GTD include the exaggerated placental site and the placental site nodule or plaque. Both lesions are proliferations of the intermediate trophoblast. Staging of GTD should only be applied in cases of persistent disease. All different staging systems, including the revised FIGO system, the classification of the National Institute of Health (NIH), the WHO scoring system and the currently adopted TNM-system are able to define high risk patients.